1. Field of the Invention
The present invention relates to a control technique of a power source circuit that converts a commercial power source to a power source such as a home appliance machine.
2. Description of the Related Art
The present applicant has disclosed a conventional power source apparatus having a boost chopper-type power factor improvement and a harmonic current suppression function. In the conventional power source apparatus, to improve a power factor, when converting an input power to a DC voltage and obtaining a load voltage with a boost chopper circuit, a switching element of the boost chopper circuit is switched to flow short-circuit current via a reactor (boost choke coil). A controller that controls the power source apparatus turns ON or OFF the switching element based on a comparison result between a detected input current by an input current detector and a sinusoidal wave-like input current reference signal. The controller that controls the power source apparatus also switches, for every a half cycle of an AC power source, the switching element a predetermined number of times based on the detection of a zero cross by a power-source phase detection circuit. Thereafter, the switching of the switching element is prohibited to prevent the number of switchings for every half cycle of the AC power source from fluctuating.
The conventional power source apparatus is structured to perform a switching in a former half of the half cycle of the AC power source to improve a power factor to suppress a harmonic current. As a result, the conventional power source apparatus has achieves, for example, the following effects:                (1) the small number of switchings causes a reduced heat burden to a switching element such as an IGBT or a reverse blocking diode to reduce the size;        (2) the low switching frequency band causes reduced noise and thus less components for reducing noise are required; and        (3) reduced harmonic current allows low-cost material to be used for a reactor core.        
FIG. 14 depicts a waveform of an input current and an instantaneous average value of a switching interval in the conventional power source apparatus (hereinafter, “conventional system”). A power source harmonic standard specifies up to 40-th harmonic currents (up to 2 kilo Hertz (kHz) for a power source of 50 Hertz (Hz) and up to 2.4 kHz for a power source of 60 Hz). Thus, when a switching basic frequency in a switching interval is equal to or higher than this, current in the switching interval is handled as an instantaneous average value in the manner represented by dotted lines in the drawing.
When the current is considered as an instantaneous average value as described above, a current waveform of an actual measurement value at an input current of 16 Arms is as shown in FIG. 15. The harmonic current value of the current waveform shown in FIG. 15 has an actual measurement value as shown in FIG. 16.
In FIG. 16, the horizontal axis represents a harmonic order n and the vertical axis represents a harmonic current value by the measurement using a reactor inductance of about 20 mH and input current of about 16 Arms. The bar graph represent a measurement result of harmonic current and the line graph shows values of the table 1 of the power source harmonic standard IEC61000-3-2.
When the 2-nd to 40-th harmonic current values shown in FIG. 16 are standardized by limit values shown in the table 1 of IEC61000-3-2, the result is as shown in FIG. 17. In FIG. 17, the horizontal axis represents a harmonic order n while the vertical axis represents an n-th harmonic rating exponent Yn as a standardized current value.
As shown in FIG. 17, in the conventional system, a high current region of about 16 Arms shows an increase of a 5-th harmonic unique to a partial switching PFC and a n-th harmonic exponent Yn exceeds 1, failing to clear the power source harmonic standard. Moreover, a current region of about 12 to 15 Arms also requires a high reactor inductance in order to satisfy the power source harmonic standard, thus increasing the cost of the power source apparatus.